Metallizing coating compositions containing coated metal flakes

ABSTRACT

METALLIZING COATING COMPOSITIONS HAVING GREATER SPARKLE AND GLITTER ARE FORMED BY INCLUDING IN THE COATING COMPOSITION INSOLUBLE RESIN-SUPPORTED PLANAR REFLECTIVE METAL FLAKES IN AN AMOUNT OF FROM ABOUT 0.003% TO ABOUT 0.035% OF METAL (PARTICULARLY ALUMINUM) BASED ON THE WEIGHT OF THE COMPOSITION. THE FLAKES ARE SUPPORTED AND RENDERED MORE PLANAR BY USING A METAL FILM SURFACED ON BOTH SIDES WITH A RELATIVELY INSOLUBLE RESINOUS FILM HAVING A THICKNESS OF AT LEAST 0.01 MIL. WHEN THE SUPPORTED METAL FILM IS BROKEN UP TO FORM FLAKES, THE FLAKES ARE FLATTER AND REFLECT LIGHT OVER A LARGER PORTION OF THEIR SURFACE TO PERMIT USE IN SMALLER AMOUNT.

United States Patent ()1 ice 3,692,731 Patented Sept. 19, 1972 3,692,731METALLIZING COATING COMPOSITIONS CONTAINING COATED METAL FLAKES WalterR. McAdow, Grosse Pointe Farms, Mich., assignor to Mobil Oil CorporationNo Drawing. Filed Apr. 29, 1970, Ser. No. 33,106 Int. Cl. C08g 51/04,51/34 U.S. Cl. 260-323 R 12 Claims ABSTRACT OF THE DISCLOSURE'Metallizing coating compositions having greater sparkle and glitter areformed by including in the coating composition insoluble resin-supportedplanar reflective metal flakes in an amount of from about 0.0003% toabout 0.035% of metal (particularly aluminum) based on the weight of thecomposition. The flakes are supported and rendered more planar by usinga metal film surfaced on both sides with a relatively insoluble resinousfilm having a thickness of at least 0.01 mil. When the supported metalfilm is broken up to form flakes, the flakes are flatter and reflectlight over a larger portion of their surface to permit use in smalleramount.

The present invention relates to organic coatings containing separatedreflective aluminum flakes which add sparkle to the coated film.

Coatings of the general type under consideration are known anddescribed, for example, in my prior 'U.|S. Pats. 2,839,378 and 2,941,894in which vapor deposited aluminum of great covering capacity is brokenup and incorporated in a film forming coating vehicle. In said Pat.2,941,894, the aluminum is used in amounts of from 0.028% to 0.15%aluminum, based on the weight of the composition. This proportion ofaluminum was far smaller than was previously needed, but it was enoughto produce a brilliant polychromatic finish. However, in the amountsneeded to produce the desired metallic lustre, the pigmentation of thecoating was partially obscured reducing the contrast between themetallic flake and the background.

It has now been found that greater sparkle can be provided in themetallizing coating compositions under consideration if the aluminum isused in smaller amount in the form of large insoluble resin-supportedflakes of increased planarity so that a greater proportion of the flakesreflect light in unison creating more Widely separated areas exhibitingincreased sparkle. In this way, each reflecting flake shines morebrightly and there is less masking of the pigmentation of the coating.Moreover, the flakes used herein are supported on both sides by resincoatings which are relatively insoluble in the coating solution so thatthe flakes deposited at the surface of the coating and which provide thedesired glitter are protected against corrosion despite being positionedat the surface.

Curiously, and even at the lower portion of the amount of aluminumpreviously considered to be necessary, the large supported planaraluminum flakes used in this invention build on one another and protrudethrough the film which is detrimental. The usual film thicknesses forautomotive application are from 1.5-3.5 mils and it is preferred thatthe flakes used herein have a major dimension larger than the thicknessof the film.

Another problem with the known coatings is the tendency for the aluminumflakes to be attacked and dissolved away upon exposure to the elements.Where the aluminum flakes are dissolved away, the darker pigments of thecoating show through so that some portions of the surface area aredarkened due to corrosion while the remainder of the coating retains thealuminum flakes providing a mottled appearance. In the presentinvention, the relatively insoluble resin coatings on the aluminumflakes serve to increase the corrosion resistance of these flakesthereby minimizing any mottling tendency.

The aluminum flakes which are utilized in this invention are preferablyconstituted by vapor deposited aluminum which is extremely thin, as iswell known, but the flake is supported on both sides thereof by aresinous film of limited solubility in organic solvents and each ofwhich are thicker than the aluminum which is sandwiched therebetween.Preferably, the resinous film is at least 0.01 mil in thickness, morepreferably at least 0.08

' mil. While the film should generally not be so thick as to preventbreak-up using an appropriate solvent and mechanical agitation, thepreferred films do not exceed 0.2 mil in thickness.

When a film of aluminum having a thinness associated with vapordeposited aluminum is sandwiched as described and agitated in a liquidmedium comprising an organic solvent system which is not capable ofsubstantially dissolving the resin of the film, then the laminated formis retained as the overall film structure is broken up. The thin resinfilms used herein do not prevent break-up into the desired flakes, butthey protect the flakes during break-up and cause the production offlakes which are more planar than heretofore. Without these supportingresin films, the flakes at 600 magnifications are shown to besignificantly warped, e.g., they undulate or have curled edges and arewrinkled. This reduced planarity minimizes the proportion of the flakewhich can simultaneously reflect light from a given source into the eyeof a viewer. In the invention it is preferred to use flakes having adimension in excess of 30 microns, preferably in excess of 60 microns,While the largest particles are not much in excess of 200 microns. It isespecially preferred to employ flakes which have a dimension larger thanthe thickness of the coating which is formed. As a result, spaced apartflakes in the film are able to reflect the light over a relativelysubstantial surface area of the flake to provide a pronounced glitterwhich is especially useful when there are less than reflecting flakesper 5.5 square millimeters of coating so that the glittering flakes arewidely spaced. In this way the coating sparkles in the light as opposedto a more generalized metallic lustre of reduced intensity accompaniedby a partial masking of the coating pigmentation.

The supported, more planar aluminum particles used in this inventionmust be employed in very small amount in order to function, thepreferred proportions being entirely below the minimum proportion of0.028% aluminum specified in my Pat..2,941,894. Thus, preferredproportions in this invention involve from about 0.0005% to 0.025% ofaluminum, based on the weight of the composition. Even smallerproportions of aluminum on the same basis can be utilized down to about0.0003 Weight percent. In certain instances when the pigmentation isdenser or more darkly colored, it may be desired to increase theproportion of aluminum, but even here it is rarely desirable to exceedthe preferred maximum identifled hereinbefore. Moreover, the maximumproportion which can be tolerated is only about 0.035 weight percent,far less than the typical proportion used in Pat. 2,914,894. If theweight proportion of aluminum used in the persent invention is increasedbeyond the approximate upper limit specified, then the particles tend toprotrude from the coated surface which is detrimental.

While the preferred practice of the invention involves vapor depositionof aluminum to form the thin aluminum film which is desired, it will beunderstood that the specific nature of the aluminum deposition processis of secondary consideration to this invention. Thus, the film ofaluminum may be deposited in a vacuum or by electroless deposition, andso long as the aluminum film is sufficiently thick to reflect light, itcan be used in this invention. Electroless deposition is illustrated bythe de composition of aluminum hydride as described in Pat. 3,462,288.More particularly, the thickness of the aluminum film is preferably ofthe order of about 0.5 to millionths of an inch and various methods ofproducing films of this character are know as described in my said priorpatents. The thinnest aluminum films having a thickness of less than 3millionths of an inch are especially benefitted by this invention sincethese, in the absence of this invention, are more easily distorted bythe agitation used to break the film into flakes. Also, the thinnerfilms have less mass and corrode away more easily when they are at thesurface to produce a mottled appearance upon exterior exposure. Also,the combination of thin metal film and insoluble resin coatingminirnizes settling of the flakes in coating compositions containing thesame.

The supported aluminum flakes of this invention are dispersed in afilm-forming coating vehicle, the specific nature of which is ofsecondary significance. The coatings of the present invention areparticularly useful in the automotive field as a topcoat for theexterior of the automobile. In this utility, acrylic coatings are todayof especial interest and these are illustrated by solution polymerscontaining 80% to 100% of polymerized methyl methacrylate, any balanceof the polymer being monoethylenically unsaturated monomercopolymerizable with methyl methacrylate such as other alkyl esters ofacrylic or methacrylic acid illustrated by butyl acrylate. Small amountsof acrylic or methacrylic acid may be present if desired. While acrylicpolymers of the type used in automotive finishes are particularlypreferred in this invention, any lacquer, or coating polymer system, orenamel, may be utilized, whether clear or pigmented, and especially thelatter, particularly at high glass coating systems which are utilizedfor automotive topcoats. These automotive finishes frequently includecellulosics such as cellulose acetate butyrate and appropriateplasticizers. In this respect, typical acrylic automotive finishes whichmay be used are described in US. Pat. 2,849,409. My said prior patentsdisclose further coating vehicles which may be utilized, and these arealso useful in this invention.

It is desired to point out that a feature of the present invention isthe capacity to utilize the sandwiched aluminum flakes of this inventionin aqueous coating compositions. Normally, the highly reactive aluminumflakes cannot be used in normally alkaline water medium because thealuminum will react with the water. In this invention, the aluminium isprotected so that, as a result of the very small propertion of aluminumwhich is used, and the fact that the aluminum is substantiallyunavailable to the aqueous medium, the aluminum particles may beincorporated in an aqueous coating system without ill effect. In thisrespect, the aluminum sandwich is stripped from the supporting layerusing a water miscible organic solvent and the dispersion of aluminumflake in the solvent is then dispersed in the aqueous coatingcomposition.

In this invention, the aluminum film is present in a sandwich orlaminate in which both opposed surfaces of the aluminum film are coveredwith a resinous film which is generally insoluble in the liquid systemof the coating composition. The acrylic solution polymers normally usedin automative coatings as well as the other resin systems known to beuseful for such purpose, such as the alkyd resin-aminoplast resin blendsdisclosed in my Pat. 2,941,894 are soluble in one or more of theconventional solvents used in automotive finishes, e.g., mixtures ofarcmatichydrocarbons such as xylol and aliphatic hydrocarbons, such asmineral spirits or naphtha, which may be supplemented by ketones such asmethyl etheyl ketone or methyl isobutyl ketone. The resins used as acoating to surface the aluminum film on both sides thereof must berelatively insoluble in these same solvent systems. To facilitateremoval of the coated aluminum film from the substrate on which it isformed, a resin which is readily soluble in the solvents underconsideration is used as a release layer. For example, isobutylmethacrylate is a typical release coating which may be used. Rosin ormaleinized rosin or ester gum will further illustrate soluble releaselayers which may be used. Thus, a laminate is formed and laterphysically removed from its support using a solvent which dissolves therelease coating holding the laminate on the support. However, the resinsused to form the laminate are relatively insoluble and these do notdissolve in the solvent. Upon mechanically disrupting the separatedlaminate in a solvent medium, there is produced large suported flakes inwhich the resin surfacing layers remain undissolved to protect thealuminum surface against corrosion and to prevent distortion of thealuminum to improve the planarity of the support flakes which areproduced.

The thickness of the surfacing layers of resin, while of secondaryconsideration, is nonetheless significant from the standpoint ofenhancing the chemical resistance of the laminate. A coating having athickness of about .01 mil is broadly adequate to stiffen the aluminummetal flake and enable the production of the more planar flakes. On theother hand, thicker layers of resin are preferred and it is best thatthe resinous layer have a thickness of .08 mil or more in order tomaximize chemical resistance to avoid mottling on exposure andweathering.

Another feature of the invention is the fact that the resin films usedto surface the aluminum film may be dyed or pigmented to impart color tothe reflected light. Similarly, the aluminum can be colored or anodizedand the surfacing resin films can function to seal the color on thealuminum. Numerous decorative eifects will be apparent from thiscapacity to vary the color and appearance of the flakes which are used.

In the production of aluminum film laminates of the type utilized inthis invention, it is convenient to employ a support such aspolyethylene terephthalate (Mylar) and this support is then coated Witha soluble polymer layer release coating in order that this first coatingmight be easily stripped from the Mylar support upon subsequenttreatment with organic solvent. A layer of polymer of limited solubilityis then applied having a thickness as discussed hereinbefore and forcedried to remove the solvent employed to apply the same. The aluminumfilm is then applied in any convenient manner, but vapor deposition ispreferred. While the thickness of the aluminum film may varyconsiderably as has been explained, it is convenient to deposit thealuminum in an amount such that there is approximately /s pound ofaluminum per 10,000 square feet of surface (about 2 millionths of aninch). Then, a further coating of polymer layer of limited solubility isapplied, which may be the same or different from the layer on the otherside of the aluminum. This top layer is then force dried forming asandwich of two layers of relatively insoluble polymer, on on eithersurface of the film of metal. This sandwich is positioned on the Mylarsupport and retained thereon by the releasecoating. The composite ofsupport, release coating and sandwich or laminate is run through a bathof solvent (preferably acetone, which may be heated if desired) whichdissolves the release coating and the sandwich comes off the Mylarsupport (usually with the aid of mechanical manipulation supplied byrunning the composite over rollers). This provides a slurry of partiallybroken up sandwich in organic solvent and this slurry is mixed with astirrer to break up the sandwich, Without delamination, into flakes ofdesired size. Simple stirring is normally adequate to break up thesandwich into flakes, but higher speed agitation may be used if simplestirring proves inadequate.

'Ihe relatively insoluble resins which are contemplated for surfacingthe aluminum film in order to produce the laminate or sandwich which isdesired are subject to considerable variation so long as they arerelatively insoluble in ordinary organic solvents of the type which maybe utilized to remove the laminate from the support on which it wasformed an to dissolve the resins to be used in the ultimate coatingcomposition. To illustrate these relatively insoluble resins, referenceis made to copolymers containing 50-80% acrylonitrile, the balance ofthe copolymer being illustrated by ethyl acrylate. These copolymers aresoluble in relatively strong solvents such as dimethyl formamide, butthey will not dissolve in the more conventional solvents of lesseractivity such as acetone. Similarly, polyvinyl butyral is relativelyinsoluble in aromatic solvents and ketones, and it may be dissolved andapplied using alcoholic solvents. Moreover, Mylar itself is soluble inlow concentration in cresylic acids and can be applied from solutiontherein.

It should be understood that while the resins utilized to surface theopposite surfaces of the aluminum film must be insoluble in the solventwhich is utilized, this does not preclude limited swelling of the resinin the solvent medium. In this respect, it will be appreciated that theresin films are not intended to prevent break-up of the releasedlaminate into flakes and limited swelling of the resin film in thesolvent medium may enhance resin break-up.

Insofar as application of the resin film is concerned, the resin ispreferably applied from solvent solution medium followed by removal ofthe solvent by volatilization (preferably using force drying in whichheated air is blown over the wet coating to dry the same). Curingconditions for a limited thermosetting cure may be used, assuming thesupport and the release coating can Withstand the temperatures involved.Relatively strong solvents may be used for application since they arerapidly evaporated so as to avoid unduly injuring the supportingmaterials.

The concentration of resin in the solvent solution helps to determinethe thickness of the films. Since thin films are desired, low solidscontent solutions are preferred, e.g., 3-15% solids.

The present invention will be illustrated by a composite in which alayer of polyethylene terephthalate film 0.69 mil thick (Mylar) is firstsurfaced with a release coating constituted by polyisobutylmethacrylate. If desired, one may instead use a copolymer of methylmethacrylate and isobutyl acrylate in a weight ratio of 92/ 8. Also, onemay use ma'leic modified ester gum or rosin or gelatin.

After the release coating has been dried, a 0.10-0.15 mil thick film ofa copolymer of 40% ethyl acrylate and 60% acrylonitrile is depositedthereover. This copolymer may be made by copolymerizing the monomers at25% solids in solution in dimethyl formamide in the presence of 1%benzoyl peroxide catalyst, the reaction being carried out at reflux for8 hours. The solution of resin soobtained is then diluted withadditional dimethyl formamide to a viscosity enabling roll coatapplication and the coating is force dried.

After drying, the layer of ethyl acrylate/acrylonitrile copolymer issurfaced with a vapor deposited aluminum film weighing A; pound per10,000 square feet whereupon a top layer of the same ethylacrylate/acrylonitrile copolymer is applied in the same way in athickness of 0.10-0.15 mil.

The result is a composite which can be removed by running the samethrough an appropriate organic solvent (acetone) with the compositebeing run under and over rolls or bars to help the resin-coated aluminumfilm sandwich to separate from the Mylar support. Thereafter,

ordinary agitation can be utilized to reduce the supported aluminumflakes to desired size.

In the preferred practice of this invention, agitation is continueduntil about by weight of the flakes have a major dimension in the rangeof 30-80 microns.

In place of the ethyl acrylate/acrylonitrile copolymer noted above, onemay use a 5% solution of polyvinyl butyral in a 50/50 weight ratiomixture of ethanol and butanol. This deposits a film which does notdissolve in the aromatic and ketone solvents used to release thesandwich and dissolve the resins used in the coating compositions. UnionCarbide Corporation products XYSG and XYHL illustrate commercialproducts which may be used.

Also, one may employ a 5% solution of polyethylene terephthalate incresylic acid.

There is produced as described above a slurry of resinsupported aluminumflakes and these are dispersed in the selected coating composition in anamount to provide the weight of metal described hereinbefore. Inpreferred practice, the aluminum content of the final metallizingcoating composition is 0.01% by weight.

While the coating composition itself is subject to considerablevariation, a preferred coating composition is illustrated by combining50 parts of a methyl methacrylate copolymer with 30 parts of a polyesterplasticizer and 20 part of cellulose acetate butyrate, the solventsbeing aromatic hydrocarbons and ketones. A preferred methyl methacrylatecopolymer contains 92% of methyl methacrylate and 8% of isobutylacrylate and is supplied as a 40% solids solution in a 3/1 blend oftoluol and methyl ethyl ketone. An appropriate polyester plasticizercontains 37.7% neopentyl glycol; 22.9% pelargonic acid; 21.0%isophthalic acid; and 18.4% adipic acid. This polyester is supplied as a95% solids solution in xylene. The cellulose acetate butyrate is used asa 25% solids solution in toluol and acetone.

By mixing the three solutions in the form recited, a preferred coatingvehicle is obtained. If desired, a small proportion of the methylmethacrylate copolymer may be replaced by another methyl methacrylatecopolymer providing increased adhesion, e.g., a copolymer containing 79%methyl methacrylate; 8% isobutyl acrylate; 8% methacrylic acid; and 5%of an adhesion promoting agent which is subject to wide variation. Thus,the methacrylic acid can be reacted with propylene imine or glycidylmethacrylate can be used which may be aminated or ammoniated as desiredor an amine acrylate may be selected, all of these being well known toenhance the adhesion of a methacrylate coating system to a substratebase.

The solvent system for the methacrylate polymer containing the adhesionpromoting agent can be the same as that used for the methyl methacrylatepolymer which does not contain the adhesion promoter.

The coating composition may be used clear, but it is preferred topigment the same in accordance with conventional practice.

The invention is of particular interest to pigmented coatings in which apigment is dispersed in the coating composition to provide a desirablebackground for the reflective aluminum flakes which are relied upon forbrilliance and sparkle. Appropriate pigments for coating compositionsare well known, the pigments more usually employed in the formation ofautomotive coatings including carbon black, phthalocyanine green,phthalocyanine blue, ferrite yellow, red iron oxide, titanium dioxide,iron blue, chromium tetrahydrate, lead chromate and indanthrone blue.Numerous other pigments are also used. On the other hand, and whilepigmentation is normally present, the supported planar flakes can beemployed in clear coatings as taught herein, especially when these clearcoatings are deposited atop a previously applied pigmented coating.

The present invention has been described with particular reference tothe utilization of aluminum, since aluminum is especially preferred fromthe standpoint of its availability, the ease with which it can be vapordeposited or otherwise manipulated and because of its high reflectivityin the extreme thinness under consideration. On the other hand, othermetals capable of providing reflective surfaces when deposited in thethinness under consideration can also be used. Among these metals may bementioned silver, copper, gold, tin, nickel, chromium, palladium,platinum, rhodium, and alloys of the foregoing.

it is also of interest to note that the resin-surfaced aluminum flakesused in this invention are insulated from one another and, as a result,coating compositions containing the same can be subjected to a highvoltage electrostatic charge without arcing. This has significance inthe automotive industry where electrostatic coating processes arefrequently used. The compositions of the invention may even be atomizedelectrostatically as part of the electrostatic coating process.

The invention is defined in the claims which follow.

I claim:

1. A metallizing coating composition comprising a filmforming coatingvehicle, and resin-supported reflective metal flakes of improvedplanarity dispersed therein in an amount of from about 0.0003% to about0.035% of metal, based on the weight of the composition, said flakeshaving a planar dimension in excess of 30 microns and being constitutedby a thin reflective film of metal having a thickness less than 30millionths of an inch surfaced on both sides with resinous films eachhaving a thickness which is thicker than the film of metal, the resin ofsaid films being relatively insoluble in said coating composition andbeing applied to said film of metal to form a sandwich which is brokenup to form said resin-supported flakes, whereby said flakes, in adeposited coating, form spaced apart planar flakes capable of reflectinglight over a substantial surface area thereof to provide a pronouncedglitter from widely spaced points on the surface of the coating.

2. A coating composition as recited in claim 1 in which said metalflakes are constituted by resin-supported film of aluminum.

3. A coating composition as recited in claim 2 in which said aluminumfilm is formed by vapor deposition.

4. A coating composition as recited in claim 1 in 8 which saidrelatively insoluble resin films have a thickness of at least 0.01 mil.

5. A coating composition as recited in claim 1 in which said relativelyinsoluble resin films have a thickness of at least 0.08 mil.

6. A coating composition as recited in claim 1 in which said coatingvehicle has pigment dispersed therein.

7. A coating composition as recited in claim 1 in which said metalflakes are constituted by a film of aluminum surfaced on both sides withresin films insoluble in acetone and said flakes are dispersed in acoating composition comprising aromatic hydrocarbon solvent and ketonesolvent and organic film-forming resin dissolved therein.

8. A coating composition as recited in claim 7 in which said flakes arepresent in an amount of from about 0.0005 to 0.025%, based on the weightof the composition.

9. A coating composition as recited in claim 7 in which saidfilm-forming resin comprises a solution polymer containing at least 80%of polymerized methyl methacrylate.

10. A coating composition as recited in claim 1 in which said flakeshave a dimension in excess of microns.

11. A coating composition as recited in claim 10 in which said flakesare based on an aluminum film having a thickness of the order of about0.5 to 5 millionths of an inch.

12. A coating composition as recited in claim 1 in which said coatingcomposition is an aqueous coating composition.

References Cited UNITED STATES PATENTS 3,300,329 1/ 1967 Arsino et a1117-49 3,167,525 l/l965 Thomas 260-41 3,389,105 6/1968 Bolger 260-232,893,378 6/1958 McAdow -.5 2,941,894 6/1960 McAdOW 106-193 2,947,6468/1960 Devany et al 106-193 MORRIS LIEBMAN, Primary Examiner R. ZAITLEN,Assistant Examiner US. Cl. X.R.

106-290; 117-100; 260-37 M, 39 M, 41 B *Z2;;g TED STATES PATENT OFFICECERTIFICATE OF CORRECTION Patent 3,692,731 Dated September 19, 1972Inventor(s) Walter R. McAdow It is certified that error appears in theabove-identified patent and that said Letters Patent are herebycorrected as shown below:

Column 2, line 65, change "2,9l l58 9 U' to -2,9 ll',89 L-- Column 3,line ll, change "know to --known- I Column 3, line] 56, change"propertion" to "proportion-- Column L, line 23, change "support" to-supported Column L, line 63, first occurrence of "on" should read--one---' Column 5, line 11, "an" should read "and-- Signed and sealed.this 1st da of May 1973 (SEAL) Attest:

EDWAi-lDl I. FLETCHER, JR; ROBERT GOTTSCHALK Attesting OfficerCommissioner of Patents

